Integrated circuit devices are typically formed by mounting an integrated circuit chip on a lead frame and coupling these two elements to form an assembly. The integrated circuit chip and lead frame may be encapsulated. Typically, the chip includes a number of bond pads that may be positioned about the chip according to a predetermined spacing. The lead frame typically includes a number of leads about a perimeter thereof. One type of lead frame, for example, has a generally rectangular shape with each side of the rectangle having a number of leads. Typically, the leads have a relatively narrow elongated shape with a longitudinal axis that is generally perpendicular to the side of the lead frame on which the lead is located. A lead frame may be said to have an X and Y axis. Therefore, leads on one pair of opposing sides of the lead frame have longitudinal axes extending generally in the X-axis direction. Leads on the other pair of opposing sides of the lead frame have longitudinal axes extending generally in the Y-axis direction. Some leads may have longitudinal axes that are offset from the X-axis and Y-axis directions.
To couple the integrated circuit chip to the leads of the lead frame electrically, a wire bonding technique is often used. A wire bonding machine may have a spool of a bonding wire mounted on the machine. The bonding wire may be threaded through a capillary mounted to an ultrasonic horn of the wire bonding machine. The horn may be manipulated to move the capillary both vertically and horizontally. Typically, the wire bonding machine includes a device for heating or applying a spark to an end of the bonding wire that protrudes from an exit end of the capillary. The molten wire may form the shape of a ball that is placed on a target bond pad by manipulating the horn to move the capillary.
After this bond pad bond is created, a sufficient amount of bonding wire is released to allow the capillary to be moved to a location near an inner end of a target lead of the lead frame. The capillary is manipulated to connect the bonding wire to the inner end of the target lead and partially cut the bonding wire so bonding wire can be drawn from the exit end of the capillary as the capillary is raised by the horn until a sufficient length of bond wire protrudes from the exit end of the capillary in preparation to break the bond wire at the partially cut portion of the bond wire. The end of the bond wire is now free to form a new bond between a new target bond pad and target lead. Any type of suitable bond may be made at either the bond pad or the lead, including ball bonds, stitch bonds, and wedge bonds. A ball bond may be used, for example, at the bond pad. A stitch bond may be used, for example, at the lead. To complement the bonding process, the assembly components may be heated. Also, ultrasonic energy may be applied.
Problems in wire bonding techniques arise in part from the desire to increase the number of bond pads and leads in a given assembly and to make lead frame/chip assemblies smaller and smaller. This may require that the bonding pads located on the chip be made smaller and be spaced closer together. The same can be said for the leads on a lead frame.
The exit end of a wire bonding capillary is often called the capillary face. Previous capillaries have had a circular face. A disadvantage of having a capillary with a circular face is that the spacing between bonds is limited. After a bond is made at a particular bond pad, for example, if the adjacent bond pad is too close, then the capillary face may strike the ball bond that has been made at a first bond pad during the process of making a bond on an adjacent bond pad.
One method for solving this shortcoming is to use a wire bonding capillary with a non-circular face. This type of approach is shown, for example, in U.S. Pat. No. 5,544,804 issued to Test, et al., which is hereby incorporated by reference for all purposes. Test, et al. shows a capillary having a non-circular face. The face of the capillary may have a shape that includes a pair of opposed convex sides joining a pair of opposed concave sides. The capillary may be generally described as having a longitudinal axis extending across the midpoints of the convex sides and through its center. The capillary allows ball bonds, for example, to be made closer to one another than with a circular capillary face. The capillary can also make strong stitch bonds. Typically, the stitch bond is made by the capillary having its longitudinal axis generally oriented along the longitudinal axis of the target lead. Some wire bonding machines, known generally as dual-headed bonding machines, utilize two such capillaries. One capillary is used to make the ball and stitch bonds in the X-axis direction of a given assembly and the other capillary is used to make the ball and stitch bonds in the Y-axis direction of the assembly.
A problem arising in this situation is that not all bonding machines are dual-headed bonding machines. Instead, there are single-headed bonding machines that have one capillary aligned in one direction. While this type of set up can make bonds in one direction, due to the noncircular face of the capillary, they cannot make adequate bonds in the other direction without some sort of modification to the bonder or the capillary. Thus, a need exists for a method of making integrated circuit devices using a capillary with a non-circular face in single-headed bonding machines.